It's similar to what you can do in Julia, but there you use this syntax only for one-liner functions. The problem with this function declaration is that you need read up to the '= do' combo in order to understand that you're in a function definition. A keyword in the beginning would make it much easier.

I'd love to hear what features CoffeeScript made appear in other languages. JS did not take the syntax at all. I guess it's hard to tell whether generators and var-args came from CS or Python.